1. Field of the Invention
The present invention relates to a substrate processing apparatus for applying given processing to a substrate while rotating the substrate.
2. Description of the Background Art
Substrate processing apparatuss are used to apply various processings, such as processing for applying processing liquid like photoresist liquid, developing processing, cleaning processing, etc., to substrates such as semiconductor wafers, glass substrates for use in liquid-crystal display devices, glass substrates for photomasks, glass substrates for optical disks, etc.
For example, a spin coater applies processing liquid like photoresist onto a substrate while horizontally supporting and rotating the substrate. A spin developer supplies developer onto a substrate while horizontally supporting and rotating the substrate.
FIG. 22 is a schematic sectional view showing an example of a conventional substrate processing apparatus. The substrate processing apparatus shown in FIG. 22 is a spin coater.
In FIG. 22, the substrate processing apparatus has a spin holder (a spin chuck) 1 for holding a substrate W by vacuum suction. The spin holder 1 is attached on the top end of a rotating shaft 2 of a motor (not shown) and is rotation-driven around the vertical axis.
A splash-guarding cup 4 is provided to surround the substrate W held on the spin holder 1. This cup 4 is formed of an upper cup 4a and a lower cup 4b. The upper cup 4a is attached to the lower cup 4b in a detachable manner. The upper cup 4a has an opening 13 and the lower cup 4b has a waste fluid outlet 8 and a plurality of gas exhaust holes 7 in its lower part. The gas exhaust holes 7 are connected to a gas exhaust system in the factory.
An internal cup 6 is provided below the spin holder 1. This internal cup 6 has an inclined surface which is inclined down outwardly.
A resist nozzle 9 for discharging resist liquid onto the substrate W is provided above the spin holder 1. The resist nozzle 9 can be moved up and down and also can be moved between the position above the substrate W and a stand-by position outside the cup 4. Provided under the substrate W are a plurality of back side cleaning nozzles 11 for discharging rinse liquid for cleaning the back side of the substrate W.
When applying resist liquid, a flow of clean air is supplied from above toward the surface of the substrate W through the opening 13 of the upper cup 4a. The resist liquid is discharged from the resist nozzle 9 onto the substrate W supported on the spin holder 1, which spreads over the entire surface of the substrate W as the substrate W rotates.
At this time, surplus resist liquid is splashed away from the substrate W by centrifugal force developed as the substrate W rotates and attaches to the inner wall of the cup 4. Part of the resist liquid attached on the inner wall of the cup 4 remains attached, and the remaining part flows down along the inner surface of the cup 4 and is discharged outside through the waste fluid outlet 8.
Further, when the resist liquid strikes the inner wall of the cup 4, part of it becomes mist due to the impact. The mist floats on the rotating flow produced in the cup 4 as the substrate W rotates. The mist floating in the cup 4 comes down along the inclined surface of the internal cup 6 from around the substrate W with the clean air flow supplied from above. It is then drawn into the gas exhaust holes 7 under the bottom side of the internal cup 6 and exhausted by an external exhausting system.
After the resist liquid has been applied, rinse liquid is discharged toward the back side of the substrate W from the back side cleaning nozzles 11 to clean the back side of the substrate W.
Recently, with spin coaters, there is a tendency to increase the rotating speed of the substrate W when spreading resist liquid for the purpose of saving the resist. Also, when using special resist liquid having high viscosity with a spin coater, the substrate W is rotated at increased speed to spread the resist liquid so that the thickness of the resist film can be controlled thin.
However, as the substrate W is rotated at higher speed, the air flow in the cup 4 is disturbed more violently, or the resist liquid is splashed away to become mist at higher rate. As the result, the absolute amount of mist in the cup 4 increases.
The spin holder 1 of the conventional substrate processing apparatus is formed of synthetic resin, such as PEEK (Poly-ether-ether-ketone), Teflon, polyacetal, etc. Since these synthetic resins have inferior elasticity as compared with rubber, fine vacuum leakage occurs at the suction surface between the spin holder 1 and the substrate W, as shown by the arrows in FIG. 23.
Particularly, when substrates W pass through thermal treatment process, for example, the individual substrates W will be warped with different tendencies. In such a case, when the substrates W are processed in the spin coater, the leakage from the suction surface between the spin holder 1 and the substrates W will occur more seriously.
Conventionally, since a substrate W was rotated at relatively low rotating speed in the spin coater, only a small amount of mist was produced around the substrate W. Therefore only a small amount of mist was drawn by the leakage from the suction surface between the spin holder 1 and the substrate W.
However, as the rotating speed of the substrate W increases, the absolute amount of mist increases as stated above, and an increased amount of mist is then drawn by the leakage from the suction surface of the spin holder 1 and the substrate W. As a result, the drawn mist will attach to the back side of the substrate W in the vicinity of the periphery of the spin holder 1. The mist attached to the back side of the substrate W dries to form particles to contaminate the back side of the substrate W. The contaminated back side of the substrate W will cause inferior focusing in exposure processing.
Although the contamination on the back side of the substrate W can be cleaned away with the rinse liquid delivered from the back side cleaning nozzles 11, the rinse liquid cannot be delivered toward the periphery of the spin holder 1, because penetration of the rinse liquid into the spin holder 1 is not desirable. Accordingly, it is difficult to completely remove the mist attached on the back side of the substrate W in the vicinity of the periphery of the spin holder 1.